This invention relates to an internal combustion engine intake system, and more particularly to an intake system comprising an extra induction passage which terminates at a jet-producing nozzle opening into an intake port portion of a usual induction passage with a view of effecting improvements on combustion characteristics.
In current internal combustion engines, particularly in automotive engines, it is familiar to employ a considerably lean mixture with the object of reducing the emission of HC, CO and NOx all together or to recirculate a portion of the exhaust gas through the combustion chambers in order to suppress the formation of NOx. In either case, however, there is a strong tendency that the combustion in the engine becomes less stable and less efficient with the result that the engine operates unstably in certain ranges of practical operation conditions. Generally, it is necessary to feed the engine operating under low-load conditions or idling with a rich mixture (also at cold starting of the engine), though this brings about a difficulty in reducing the emission of HC and CO, because combustion becomes unstable under such operating conditions.
For these and other reasons, it is impermissible to optionally prescribe either the air-fuel ratio or the rate of exhaust gas recirculation solely with a view to attaining success in emission control. It is a requisite to give a careful consideration to the unfavorable influence of raising the air-fuel ratio or augmenting the exhaust gas recirculation on the stableness of combustion thereby to maintain the engine performance on a satisfactory level. However, this requirement has imposed limitations to the emission control by a relatively simple measure such as the adoption of a lean mixture or the recirculation of exhaust gas.